Field of the Invention
The present invention relates to a variable shape mirror, an apparatus such as an adaptive optics system using the same, and a method of manufacturing the same.
Description of the Related Art
A movable mirror and a variable shape mirror of a type to be displaced by an electrostatic attractive force are expected to be applied to various fields utilizing light. For example, the movable mirror and the variable shape mirror each can be utilized as an adaptive optics wavefront correction device to be installed in a fundus inspection apparatus, an astronomical telescope, or the like. As a representative example of such a movable mirror whose reflective surface is displaced by an electrostatic attractive force, there is known a measure of enabling movement by using two parallel plate electrodes, but this parallel plate type has a disadvantage in that the moving amount is small and the displacing direction is one direction that is perpendicular to the reflective surface.
In contrast, in recent years, a variable shape mirror that uses a comb electrode structure and can achieve a larger moving amount has been proposed. An example thereof is disclosed in U.S. Pat. No. 6,384,952. As illustrated in FIG. 10, in a variable shape mirror 500, a support portion 530 that supports a comb electrode 520 on a movable side and a support portion 570 that supports a comb electrode 510 on a fixed side are respectively located in the drawing sheet on upper and lower sides in a perpendicular direction. The movable comb electrode and the fixed comb electrode are opposed to each other, and are arranged so as to be alternately arrayed with a distance. With this, an electrode overlapping area larger than that in the parallel plate type can be achieved. Therefore, a larger electrostatic attractive force can be generated between the comb electrodes, and thus a moving amount of a connecting portion 540 connected to a reflective portion 550 can be increased.
Further, in Japanese Patent Application Laid-Open No. 2013-148707, there is disclosed an exemplary structure of displacement in two directions perpendicular to a reflective surface. As illustrated in FIG. 11A and FIG. 11B, in this variable shape mirror, both a movable comb electrode 1001 and a fixed comb electrode 1002 are electrically divided in a Z direction. Therefore, even when the two electrodes are at the same level, non-overlapping parts are made by applying a voltage, and a displacement force in two directions perpendicular to a reflective portion 903 (±Z directions) can be applied to a movable portion 1003.
In the above-mentioned related-art variable shape mirror of an electrostatic vertical comb electrode type having the structure disclosed in U.S. Pat. No. 6,384,952 illustrated in FIG. 10, when the mirror is driven, displacement occurs in one direction perpendicular to the reflective surface. Specifically, in this variable shape mirror, when an electrostatic actuator is driven, the mirror is displaced only in one direction that extends toward the actuator side and is perpendicular to a reference plane (on the −Z direction side), provided that the a reference plane is at a level of the mirror when the actuator is not driven with no voltage applied thereto. When the mirror is used as an adaptive optics wavefront correction device or the like, if the direction is limited to only one, a large movable amount and a large drive voltage are sometimes necessary for reducing a residual aberration. A structure is thus required in which, in addition to the related-art driving direction, driving in an opposite direction is possible.
Meanwhile, in the above-mentioned example in Japanese Patent Application Laid-Open No. 2013-148707 illustrated in FIG. 11A and FIG. 11B, the displacement force can be applied in the two directions perpendicular to the reflective portion 903. However, the movable comb electrode 1001 and the fixed comb electrode 1002 are electrically divided in the Z direction, which complicates the structure and makes it difficult to manufacture the structure. Further, it is necessary to apply different voltages to upper and lower electrode portions of the movable comb electrode 1001, respectively using a spring 1004, and thus, the spring 1004 has at least three layers and stiffness of the spring 1004 tends to become higher. Therefore, a force generated for the purpose of obtaining a movable amount necessary for the movable portion 1003 and the reflective portion 903 becomes stronger, and the drive voltage tends to become larger.